1. Field of the Invention
This invention relates to a rotary die moulding machine, and in particular to a plastic insert or wafer on a die roll of a rotary die moulding machine used for making cookies, biscuits and other baked goods.
2. Background of the Related Technology
Commercial bakeries typically produce baked goods like cookies and biscuits on a conveyor line or production line on which the goods are moulded and baked on a conveyor system. One known and often used device for moulding bakery dough is a rotary die moulding machine. The machine force feeds the dough into an engraved cavity on a die roll to mould it with the desired shape, thickness and design, and then removes the moulded dough blank from the die roll and transfers it to a conveyor oven.
On the rotary die moulding machine, bakery dough is introduced between a forcing roll and the die roll. The die roll, which is the heart of the rotary die moulding machine, is a long metal cylinder which extends across the width of the conveyor. The die roll, normally made from bronze, may be one piece or made in sections and it has engraved into its outer surface a number of cavities in the shape and design of the baked good to be moulded. The dough is forced into the engraved cavities on the die roll thereby moulding the dough into the desired shape and thickness and imprinting it with a design. Excess dough is trimmed with a shear knife. The moulded dough blank is then extracted from the cavity by pressing it against a fabric extraction web which releases it from the die and then transfers it to an intermediate web for deposit onto a baking band and into an oven for baking.
Sandwich cookies such as OREOS.RTM. are commonly produced by this process. Rotary die moulding machines are used to make a wide variety of shapes, designs and thicknesses of baked goods.
Despite being widely accepted by high production commercial bakeries, rotary die moulding machines have a number of disadvantages and objectionable features. The engraved design in the cavity may become roughened or slightly pitted due to the action of soda or ammonia and other ingredients in the dough or by foreign objects inadvertently introduced into the machine. Furthermore, bakery dough has a tendency to stick to particularly intricate designs engraved into the cavity. For these reasons the dough blank occasionally does not release well from the cavity in the die roll, causing an accumulation of dough and greatly reducing the definition of the detailed engraving imprinted on the baked product. This results in difficulty in maintaining the specified weight of the baked product as well as objectionable visual blemishes on the surface.
TEFLON.RTM. or other nonstick surface treatments have been applied to die rolls in an effort to improve release characteristics. Nonstick coatings, however, wear off, especially when rougher types of bakery dough are used. Reapplication of a nonstick coating is possible, but reapplication requires removal of all the old coating. Removal and reapplication of coatings requires that the die roll, shaft, and hubs be completely disassembled, thoroughly cleaned by blasting with glass beads, cavities de-burred, coated, heat treated, excess coating on the outer surface of the die roll removed and re-assembled. This process typically takes the die roll out of service two to three weeks, and costs 12 to 15 percent of the cost of a new die.
An engraved die roll is also expensive to make, and, if only one of the engraved cavities becomes disfigured, replacement of the entire die roll may be required. In an effort to reduce cost, one known system provides a replaceable metal insert for the die cavities, depicted in FIG. 8 of the drawings. On this known system, the die roll cavity is formed as a simple bore with straight sides. The metal insert is placed into the cavity and, from within the center of the die roll, bolted into the bore. In the event a foreign object disfigures the designed face on a particular metal insert, the metal insert may be replaced. However, replacement of the metal insert requires an extensive amount of labor to access the center of the roll to unbolt the insert and install a new one. After replacing the insert(s), the die surface must then be machined on a lathe to ensure that the new inserts are at the same surface level as the others, which may be different because of wear. Further, bakery dough and shortening have a tendency to be forced into the crevice between the bore wall of the cavity and the side of the insert, which is extremely difficult to remove and causes a sanitary problem.